1. Field of the Invention
The present invention relates generally to contact printers, and more particularly to contact printers having mechanisms for lowering a slide. A type of contact printer is known from German Offenlegungsschrift No. 3,234,515, wherein its slide can be lowered in its wound-up condition. Consequently, the printer is easier and more convenient to operate, because the operator may stand in front of the front edge of the housing and has only to bend forwardly over the glass plate to lay the printing copies in place. The printing copies commonly comprise a master copy (usually a film negative) and then a photographic element (for example, an unexposed offset printing plate). The slide, if it were in a raised position, would impede this manner of loading the contact printer.
However, a disadvantage of the above known design is that the kinematics of the movement of the slide is complicated. The slide is fastened on both sides to shifting rods which extend downwardly and which are guided vertically in sliding pieces which are themselves displaceable along the guide rails. An end of each shifting rod is connected to a link of an endless chain which revolves over a plurality of deflecting wheels so that the chain has both an approximately horizontal strand and a vertical strand.
When the connecting chain link moves in the horizontal section, the slide is moved horizontally at constant height over the glass plate, and when the connecting chain link moves downwardly along the vertical strand, the horizontal movement of the slide ceases and the slide moves only downwardly by a corresponding distance.
The double cross-guides and the chain kinematics make this known design complicated and maintenance-intensive.